Performance-enhancing drugs (PEDs) alter the body through several distinct pathways depending on the type of substance used. Some force muscles to grow faster, others increase the oxygen-carrying capacity of blood, and still others manipulate hormones that control fat storage and recovery. The effects range from rapid gains in strength and endurance to serious damage to the heart, liver, and hormonal system.
The Main Categories of PEDs
The World Anti-Doping Agency groups prohibited substances into several broad categories: anabolic agents (like testosterone and synthetic steroids), peptide hormones and growth factors (like human growth hormone and EPO), stimulants, beta-2 agonists, hormone modulators, diuretics, and masking agents. Prohibited methods also exist, including blood manipulation and gene doping. Each category works through different biological mechanisms, and each carries its own set of risks.
How Anabolic Steroids Build Muscle
Anabolic steroids are synthetic versions of testosterone. They increase muscle protein synthesis through two main routes. The first is a slower, gene-level process: the steroid binds to androgen receptors inside muscle cells, travels to the nucleus, and switches on genes responsible for protein building and satellite cell growth. Satellite cells are the repair crew for muscle tissue, and steroids both increase their number and accelerate their activity. At the same time, steroids dial down genes involved in muscle breakdown.
The second route works within minutes. Steroids bind to receptors on cell membranes and trigger rapid signaling cascades that activate a key protein-building regulator called mTORc1. This is the same pathway activated by resistance exercise, which is why combining steroids with weight training produces effects greater than either alone. The result is faster muscle repair, less cell death in muscle tissue, and accelerated hypertrophy.
Cardiovascular Damage
The heart is a muscle, and it responds to anabolic steroids the same way skeletal muscle does: it grows. Unlike bigger biceps, a thicker heart is dangerous. In a study of amateur strength athletes, a single steroid cycle lasting about 16 weeks increased the mass of the left ventricle by an average of 28 grams. The walls of the heart thickened measurably, with the back wall gaining over a millimeter and the septum (the divider between chambers) gaining nearly a millimeter.
That thickening comes with functional costs. The heart’s pumping efficiency, measured as ejection fraction, dropped by about 5% over one cycle. The heart also became stiffer, meaning it couldn’t relax and fill with blood as effectively between beats. The left atrium, the chamber that feeds blood into the ventricle, enlarged by about 9 milliliters to compensate. These changes were dose-dependent: higher weekly steroid doses produced more thickening. The encouraging finding is that in this study, the structural changes reversed after steroid use stopped. But repeated cycles over years may not allow full recovery, and the cumulative effect on heart health remains a serious concern.
Steroids also raise blood pressure, increase the concentration of red blood cells (which thickens the blood), and disrupt cholesterol balance, all of which independently raise cardiovascular risk.
EPO and Blood Oxygenation
Erythropoietin (EPO) is a hormone that tells bone marrow to produce more red blood cells. When injected in healthy people at typical doping doses over 4 to 14 weeks, it pushes the hematocrit (the percentage of blood volume occupied by red cells) up to just below 50%. That increase in oxygen-carrying capacity improves aerobic performance by 8 to 12%, a massive advantage in endurance sports.
The tradeoff is thicker blood. As hematocrit climbs, blood flows less easily through small vessels. During sleep or dehydration, when heart rate drops and blood flow slows further, the risk of clots, stroke, and heart attack rises sharply. This is why EPO has been linked to sudden deaths in endurance athletes, particularly cyclists.
Growth Hormone and Fat Metabolism
Human growth hormone (HGH) has anabolic effects on muscle and bone while simultaneously breaking down fat. It triggers lipolysis, the process of pulling fatty acids out of fat cells and releasing them into the bloodstream for energy. This effect kicks in after a lag of one to two hours and peaks at three to four hours. In a fasting state, growth hormone specifically mobilizes stored fat for fuel.
This dual action, building lean tissue while stripping fat, makes HGH attractive to athletes and bodybuilders. But it also disrupts insulin sensitivity as a direct consequence of flooding the bloodstream with free fatty acids. Over time, this can push the body toward insulin resistance, a precursor to type 2 diabetes. Growth hormone also stimulates collagen deposition in tissues, which can alter the structural integrity of connective tissue in unpredictable ways.
Stimulants and the Nervous System
Stimulants like amphetamines work on the central nervous system rather than on muscle tissue directly. They increase heart rate, cardiac output, and metabolic rate. For athletes, the performance benefit comes largely from altered pain perception: stimulants allow you to push harder by masking fatigue signals. They also heighten alertness and reaction time.
The side effects reflect the same overstimulation that produces the benefits. Rapid heart rate, high blood pressure, tremors, sweating, muscle and joint pain, dilated pupils, and rapid breathing are common. At higher doses or in hot conditions, stimulants can cause confusion, delirium, and dangerously elevated body temperature. Because they override the body’s warning systems, stimulants increase the risk of pushing past safe physical limits during exercise.
Liver Toxicity From Oral Steroids
Oral anabolic steroids are processed through the liver, and many are chemically modified to survive that first pass. This modification makes them particularly hard on liver tissue. The most common form of damage is cholestasis, where bile flow is blocked or slowed. Early in the injury, liver enzyme levels (ALT) may spike, then gradually fall over weeks to months after stopping the drug. Full normalization of bloodwork can take five months or longer.
A more alarming condition called peliosis hepatis can develop with long-term oral steroid use. In this condition, blood-filled cysts form throughout the liver, making it enlarged, fragile, and deep red. The normal barrier lining of blood vessels within the liver breaks down. Most cases are detected incidentally on imaging, but in severe cases the liver can rupture, causing sudden abdominal pain and internal bleeding. Peliosis typically reverses at least partially after stopping steroids, but the risk of catastrophic rupture before detection makes it one of the more dangerous potential consequences.
Effects Specific to Women
Women’s bodies are far more sensitive to androgens, so even low doses of anabolic steroids can trigger virilization: the development of male physical characteristics. At low androgen levels, women may develop thick dark facial hair, increased body hair, oily skin, acne, and irregular periods. At moderate levels, male-pattern baldness, loss of typical female fat distribution, and decreased breast size can occur. At high androgen levels, the clitoris enlarges, the voice deepens, and muscle distribution shifts toward a male pattern.
Most of these changes reverse when androgen exposure stops. The notable exception is voice deepening, which is permanent. This is because androgens cause structural changes to the vocal cords that don’t revert once established.
Hormonal Recovery After Stopping
When you flood the body with external testosterone or its derivatives, the brain’s hormonal feedback loop shuts down natural production. The pituitary gland stops sending the signal (luteinizing hormone) that tells the testes to make testosterone. After stopping PEDs, this suppression can persist for many months to years.
The withdrawal period is difficult for most users. In a survey of 470 men who had attempted to stop anabolic steroids, about 73% reported low mood, 59% experienced tiredness, 57% had reduced sex drive, and 56% reported physical weakness. Erectile dysfunction, anxiety, depression, and even suicidal thoughts are also documented withdrawal symptoms. Only about 5% of respondents reported no symptoms at all when stopping.
The timeline for natural testosterone to recover varies widely depending on the type of steroids used, the dose, and the duration of use. Some men recover baseline hormone levels within a few months. Others remain in a state of hormone deficiency for over a year, and some never fully recover without medical intervention.